Gas generators are used in particular for inflating an inflatable safety cushion (airbag) or for triggering a seat belt pretensioner in an automobile vehicle.
Such a gas generator customarily includes a hollow body containing gas generation means, such as for example a pyrotechnic charge, as well as an electropyrotechnic initiator for triggering the generation of the gas and its escape through the apertures of a diffuser.
The initiator is electrically controlled by two electrodes, the generator including a case delimiting an aperture giving access from the outside to the electrodes of the initiator.
A retaining part is provided in the aperture between the initiator and the housing to hold them in their relative position, the electrodes crossing outward through the aperture as well as the retaining part.
Said retaining part is customarily made of overmoulded plastic.
One of the problems presented by the overmoulded part is the seal between the overmoulded part and the initiator.
Indeed, moisture must not be allowed to pass from the outside to the inner chamber of the gas generator containing the gas generation means. In particular, said moisture must not be allowed to pass along the two electrodes that are accessible from the outside and along the rest of the initiator.
Document US-A-2004/0232679 describes a gas generator, including an electropyrotechnic initiator, an assembly housing gas generator means arranged to release at least one gas following ignition of the electropyrotechnic initiator, the initiator including a case containing the pyrotechnic charge of the initiator and two electrodes jutting outside the case for electrically controlling the ignition of the pyrotechnic charge of the initiator, the initiator additionally including a cap, which caps the case on the gas generation means side, the gas generator also including a determined part delimiting a first access aperture from the outside to the electrodes of the initiator and a retaining part obtained by overmoulding plastic in the first opening between the initiator, the cap and the determined part, for retaining the initiator and maintaining the initiator in position with respect to the determined part, the electrodes crossing outward through the first aperture and the retaining part, the cap including a bottom integral with a side wall delimiting a second aperture in which the case is inserted, the wall having an outer protrusion for retaining the cap in a corresponding recess in the retaining part.
Thus, document US-A-2004/0232679 provides, for protection against moisture from the outside, for sealing the inside of the hollow body containing the gas generating material with an initiator retaining part, which is an integral part of a member welded to the hollow body. The document indicates that a seal is thus obtained between the retaining part and the hollow body. However, the document does not provide any means for preventing moisture from crossing along the electrodes and along the initiator toward the inside of the hollow body.
Initiators, the cap whereof is surrounded by a part made of plastic, are also known from documents DE-A-19914241, WO 2004/003457 and US-A-2004/0123765. These initiators require an additional separate retaining part gripping the plastic part to hold the initiator within a gas generator.
Document WO 02/36525 describes a system that allows several initiators to be held relative to a metal base by means of a metal part and of an overmoulded nylon body completely surrounding the initiator.